Method and apparatus for screening of polycondensation catalysts

ABSTRACT

The present invention relates to a method for screening of polycondensation catalysts, wherein at least two polycondensation catalysis reactions are performed simultaneously under substantially equivalent conditions in at least two reaction cells which are present in one and the same room, using a sample comprising material to be polycondensated and a catalyst to be screened, and wherein the performances of the catalysts are analyzed.  
     The present invention further relates to an apparatus suitable for performing the method.

[0001] The present invention relates to a method for screening ofpolycondensation catalysts, wherein at least two polycondensationcatalysis reactions are performed simultaneously under substantiallyequivalent conditions in at least two reaction cells, using a samplecomprising material to be polycondensated and a catalyst to be screened,and wherein the performances of the catalysts are analyzed.

[0002] Polycondensation catalysts vary in their ability to speed up thereactions for polymerizing e.g. polyesters, particularly for thoseprepared from diols and diacids (or diesters). Polycondensationreactions and catalysts are known in the field. Examples ofpolycondensation catalysts are e.g. Ti(OBu)₄, Ti(O-iPr)₄, Sb(OBu)₃,Al(O-sBu)₃, Ge(OEt)₄, etc.

[0003] In practice polycondensation catalyst are screened usingclassical laboratory equipment, e.g. glass or metal reaction vessel,stirrer, etc.

[0004] A problem of the known methods for screening polycondensationcatalysts is that laboratory screening takes about a day perpolymerization. Furthermore polycondensation catalysis reactions have tobe carried out on a scale of at least 10 g to 1000 g, commonly about 100g to 500 g. Also, results obtained using conventional screening methodsare not predictable for catalyst activities on a large, i.e. industrialscale.

[0005] The above problems are particularly pertinent when a large amountof catalysts have to be screened, especially when only a small amount ofstarting material, e.g. less than 10 g, is available.

[0006] It is an object of the present invention to avoid the aboveproblems and to provide a more efficient method for screeningpolycondensation catalysts.

[0007] It is a further object of the present invention to provide a newmethod for screening of polycondensation catalysts, that can also beused for small amounts of sample.

[0008] The above objects are achieved according to the present inventionby a method for screening of polycondensation catalysts, wherein atleast two polycondensation catalysis reactions are performedsimultaneously under substantially equivalent conditions in at least tworeaction cells, using a sample comprising material to be polycondensatedand a catalyst to be screened, and wherein the performances of thecatalysts are analyzed, wherein:

[0009] the polycondensation reactions are performed in the at least tworeaction cells which are present in one reaction room;

[0010] the reaction room is heated such that the reaction cells in thereaction room have, at least temporarily a substantially equivalenttemperature of a value>150° C.;

[0011] the reaction room is depressurized such that in the reactionroom, at least temporarily, a reduced pressure<100 mbar is maintained;and

[0012] in each separate reaction cell a pre-selected amount of sample isused in the form of a film on a surface of the reaction cell such that aratio of sample weight to reaction cell surface area covered with saidfilm of less than 1 g/cm² is obtained.

[0013] Herewith the screening of catalytic activity of polycondensationcatalysts can be performed in a surprisingly simple and efficient way.Also, the results of the screening of the method of the presentinvention are well reproducible, in contrast to conventional screeningmethods. The method of the present invention enables the simultaneouspolymerization of 2 to even more than 1000 samples under substantiallythe same conditions. As the catalytic activities of the differentcatalysts are obtained under substantially the same conditions, themethod of the present invention provides for the possibility ofdiscrimination of different catalysts.

[0014] Furthermore, the amount of sample required for eachpolymerization can be reduced to less than 10 g, to as low as less than100 mg.

[0015] According to the present invention the screening process can thusbe speeded up significantly and can be performed on a small scale. Theseresults obtained according to the present invention on a small scalealso predict, in contrast to conventional catalyst screening methods,the results to be obtained on a larger scale, i.e. in performingpolycondensation reactions on an industrial scale, as the catalysts areused in the form of a film in both the method of the present inventionand the industrial scale polycondensation reactions.

[0016] Also, no stirring of the reaction samples to promotevolatilization of water and polycondensation byproducts such as water,alcohol or glycols in order to increase molecular weight is required, asthe results of the screening method of the present invention providesrelative reactivities that can be correlated to known polymerizationexperiments. To this end one or more catalysts with known reactivity canbe included in each set of polymerizations to serve as a control orreference.

[0017] Further, variation of reaction conditions can be minimized foreach set of experiments that are conducted simultaneously. In the methodaccording to the present invention the reaction room is heated such thatthe reaction cells in the reaction room have, at least temporarily i.e.at least during the polycondensation reaction, a substantiallyequivalent temperature of a value>150° C. The person skilled in the artwill readily understand that the temperature may be changed on purposein all the reaction cells at the same time, e.g. using a temperatureprogram. Also, the reaction room may be heated such that, when thereaction room comprises different sets of reaction cells, thetemperature in the different reaction cells of one set is substantiallythe same, while the temperature between different sets may differ.

[0018] In the method according to the present invention first a samplepreparation takes place. Material to be polycondensated, such as a lowmolecular weight polyester oligomer, is doped with a certain amount ofcatalyst. This can for instance be accomplished by taking a quantity ofoligomer, adding catalyst, melting and stirring the mixture to obtain ahomogeneous “masterbatch” melt or dispersion, and then a small portionis loaded in one of the reaction cells. The person skilled in the artwill readily understand that any other suitable sample preparation maytake place instead. Also a ready-made sample may be used.

[0019] Thereafter, polycondensation reactions are performedsimultaneously in at least two reaction cells which are present in oneand the same reaction room under substantially the same conditions oftemperature, pressure, etc. as outlined above. The reaction cells areheated simultaneously to the desired reaction temperature and under thedesired vacuum. If desired, the reactions may also be conducted under astream of inert dry gas or under a stream of dry air.

[0020] An important aspect of the present invention is that only a smallamount of sample is used in each reaction cell and that the ratio ofsample weight to reaction cell surface area covered with the sample iskept low, as a film of sample is used. It has been found that herewithdiffusion of polycondensation byproducts, such as water, can be promotedresulting in an efficient polycondensation reaction.

[0021] After the polymerization reactions the performances of thecatalysts are analyzed. Analysis of the performances may for example beperformed by determining the extent of reaction. To this end IV(intrinsic viscosity), GPC (gel permeation chromatography) and NMR(nuclear magnetic resonance) measurements may, and preferably will, beconducted, for example. Of course, also other analytical methods may beused such as IR (infrared spectroscopy), color, DSC (differentialscanning calorimetry), etc.

[0022] According to the present invention it is preferred that thereaction room is heated such that the reaction cells in the reactionroom have a substantially equivalent temperature of a value between200-320° C., preferably 230-300° C.

[0023] It has been found that herewith good polycondensation reactionresults can be obtained without desintegration of the obtained products.Further, the results obtained in the different reaction cells can besuitable compared, as the conditions of p, T, . . . are substantiallythe same.

[0024] Further it is preferred according to the present invention thatthe reaction cells are arranged such that the temperature in each of theat least two reaction cells is maintained substantially equivalent.

[0025] It has been found that the temperature gradient in the reactionroom may be substantial when the reaction cells are arranged in a randomorientation, even when a heat transfer medium such as an oil bath isused in the reaction room.

[0026] Preferably the reaction room is depressurized such that, at leasttemporarily, a reduced pressure below 10 mbar is maintained, morepreferably below 5 mbar, most preferably a value between 0.01-2 mbar.Herewith diffusion of the byproducts will be such, thatcross-contamination between the different reaction cells issignificantly minimized. Also, the level of cross-contamination betweenthe reaction cells will be equal for all cells. A pressure value between0.01-2 mbar is often required at the end of the polycondensationreaction as a driving force for the reaction.

[0027] Further, the polycondensation reactions are preferably performedsuch that in each separate reaction cell a ratio of sample weight toreaction cell surface area covered with said film of less than 0.5 g/cm²is obtained, preferably of less than 0.2 g/cm².

[0028] Herewith diffusion of polycondensation byproducts, such as water,can be promoted even further, resulting in an efficient polycondensationreaction

[0029] Advantageously, in each separate reaction cell a pre-selectedamount of less than 2 g sample, preferably less than 1 g, morepreferably between 100 mg and 1 mg sample is used.

[0030] In a further aspect the present invention relates to an apparatussuitable for performing the method of the present invention, theapparatus comprising:

[0031] a sealable reaction room containing at least two reaction cells;

[0032] vacuum means for providing a reduced pressure of<100 mbar in thereaction room;

[0033] heating means for providing a substantially constant temperatureof>150° C. in the reaction cells, wherein the at least two reactioncells are arranged such that a substantially equivalent temperature insubstantially all reaction cells can be maintained.

[0034] Herewith the screening of catalytic activity of polycondensationcatalysts can be performed in a surprisingly simple and efficient way.The apparatus of the present invention enables the simultaneouspolymerization of at least 2 to even more than 1000 samples undersubstantially the same conditions. Preferably at least 5 samples, morepreferably at least 10 samples are polymerized simultaneously.Furthermore, the amount of sample required for each polymerization canbe reduced to less than 10 g, to as low as less than 100 mg.

[0035] Using the apparatus according to the present invention thescreening process can be performed in a very efficient and surprisinglysimple way. Also small amounts of starting material can be used.Further, variation of reaction conditions between different reactioncells can be minimized for each set of experiments that are conductedsimultaneously.

[0036] The reaction room containing or holding the at least two,preferably more than five reaction cells may e.g. be a self-containedblock of metal, ceramic or glass with individual cells formed within theblock. Instead the reaction room may be a holder that provides spacesfor individual, removable cells (such as vials). Preferably, removablecells are used, as they can be easily transported and weightedseparately. As an example the reaction room may be a flat- bottomedkettle with a gasket-sealed top which is connected to a vacuum pump.

[0037] As heating means preferably a heat transfer fluid bath (such asan oil bath) or a high conductivity metal block is used. Of course, anyother suitable liquid or solid heating means, such as silicone oils,molten metal salt, sand, metal shavings and the like, may be used aslong as it is stable under reaction conditions.

[0038] It has been found that the temperature gradient in the reactionroom may still be substantial when the reaction cells are arranged in arandom orientation, even when a heat transfer medium such as an oil bathis used in the reaction room.

[0039] To minimize this problem the reaction cells are, in oneembodiment of the present invention, arranged in a row. It has beenfound that the outermost reaction cells indeed may suffer from atemperature gradient, and therefore the reactions performed therein maynot be under the substantially same conditions. However, the otherreaction cells in the row do have the same temperature. These otherreaction cells may therefore suitably be used for comparingpolycondensation catalysts. The same applies for reaction cells arrangedin two rows or two sets of two rows which two sets are spaced with asuitable distance such that a substantially equivalent temperature insubstantially all reaction cells (apart from the outermost reactioncells in each rows) can be maintained. In this respect it is noted that,of course, the polycondensation reactions performed in the differentreaction cells may provide for small temperature gradients because ofthe different reactions in the different reaction cells. The sameapplies for diffusion rates.

[0040] According to an other, even more preferred embodiment of theapparatus according to the present invention, the reaction cells areplaced in a circular arrangement within the reaction room.

[0041] Herewith, in all reaction cells in the circular arrangement, asubstantially equivalent temperature can be maintained.

[0042] More polycondensation reactions may be performed at the sametime, while maintaining a substantially equivalent temperature, when thereaction cells are arranged in two concentric circles.

[0043] In order to provide a more even heat distribution when using twoconcentric circles, a well or projection may be used such that thereaction cells are placed around the projection.

[0044] An important aspect of the apparatus of the present invention istherefore that the local temperature environment of each reaction cellcan be made substantially the same, such that screening ofpolycondensation catalyst can be suitably performed. Also, the specialarrangement of the reaction cells according to the present inventionensures that cross-contamination due to differences in local temperatureand/or diffusion environments in the different reaction cells issignificantly minimized. Further, the level of cross-contamination, ifany, between the reaction cells will be substantially equal for allcells.

[0045] According to a preferred embodiment of the apparatus according tothe present invention, the at least two reaction cells are held in arack.

[0046] Herewith the reaction cells can be easily placed in the reactionroom and, after polymerization of the samples contained therein,transferred to an analyzing instrument.

[0047] The person skilled in the art will readily understand that theapparatus according to the present invention may also be used for otheruses than screening polycondensation catalysts, wherein localtemperatures in at least two different reaction cells have to besubstantially the same.

[0048] In an even further aspect the present invention relates to theuse of the apparatus according to the present invention in screening ofpolycondensation catalysts.

[0049] Hereinafter the present invention will be illustrated in moredetail by a drawing. Herein shows:

[0050]FIG. 1 a schematic cross-sectional side view of the apparatusaccording to the present invention;

[0051]FIG. 2 a schematic top view of the arrangement of the reactioncells in the apparatus of FIG. 1;

[0052]FIG. 3 a schematic cross-sectional side view of a furtherembodiment of the apparatus according to the present invention; and

[0053]FIG. 4 a schematic top view of the arrangement of the reactioncells in the apparatus of FIG. 3.

[0054]FIG. 1 shows a schematic cross-sectional side view of theapparatus 1 according to the present invention. The apparatus 1comprises a flat-bottomed kettle 2 (e.g. having an internal diameter of135 mm), which kettle 2 is sealable with a gasket top 3. In the shownembodiment, eight reaction cells 4 (e.g. vials having diameter x heigthof 25×60 mm) are present inside the kettle 2 (the ‘reaction room’),placed in a module or rack 5. The kettle 2 is connected at 6 with avacuum pump (not shown). The apparatus 1 is further provided with a heattransfer medium 7, such as sand, oil, or a massive metal block(preferably comprising aluminum or copper), to be heated during use,e.g. by an external oil bath (not shown). When a massive metal block isused, preferably a tight connection between the reaction cells and themetal block is used. In use of the apparatus 1 a substantiallyequivalent temperature in substantially all reaction cells can bemaintained.

[0055]FIG. 2 shows a schematic top view of the arrangement of the eightreaction cells 4 in the apparatus 1 of FIG. 1.

[0056]FIG. 3 shows a schematic cross-sectional side view of a furtherembodiment of the apparatus 1 according to the present invention. Theapparatus 1 comprises a flat-bottomed kettle 2 sealable with a gaskettop 3. In the shown embodiment, thirty-two reaction cells 4 are presentinside the kettle 2, placed in a module or rack 5. In the center of thebottom of the kettle 2 a well or projection 8 is present around whichthe reaction cells are placed in a circular arrangement. The kettle 2 isplaced in an oil bath 9. Using the apparatus 1, the local temperatureenvironment of each reaction cell 4 can be maintained substantially thesame.

[0057] Finally, FIG. 4 shows a schematic top view of the arrangement ofthe thirty-two reaction cells 4 in the apparatus 1 of FIG. 3.

[0058] Hereinafter the method of the present invention will beillustrated in more detail by Examples.

EXAMPLE 1 Preparation of Oligomer Samples

[0059] A 50 ml 3-neck flask with magnetic stir bar was charged with 14 gPTT (poly(trimethylene terephtalate) oligomer and 7.3 mg Ti(OBu)₄. In afume hood the reaction flask was connected to nitrogen and vacuum via aFirestone valve, degassed with nitrogen, and heated in a 240° C. oilbath. After the oligomer had melted, the reaction mixture was stirred at240° C. for about 30 minutes, cooled to room temperature and broken up.In several preparations of this type, the amount of oligomer wasincreased to about 40 g and the appropriate amount of the desiredcatalyst was added by weight or by micropipette.

EXAMPLE 2 Polymerization

[0060] An apparatus as described in FIG. 1 was used to polymerize theoligomer as prepared in Example 1, the kettle and the reaction cellshaving the dimensions given between brackets. Sand was used as the heattransfer medium.

[0061] Seven of the reaction cells (the center position was not used),being placed in a rack, were charged with about 0.5 g (corresponding toabout 0,10 g/cm²) each of oligomer/catalyst mixtures as shown inTable 1. The amount of catalyst (as ppm of metal based on weight ofoligomer) is also listed in Table 1. The rack was placed in the kettleand the kettle was sealed.

[0062] The kettle was placed in an oil bath and heated to 260° C., whilethe internal pressure was maintained under 200 mbar pressure and with aslight nitrogen sweep through the flask. When the oil bath reached 260°C., a vacuum of about 1 mbar was applied. After 3 hours the reactor wasremoved from the oil bath, filled with nitrogen and cooled.

[0063] Between 0.31 and 0.43 g product was recovered from each reactioncell and submitted for proton NMR for cyclic dimer and IV inhexafluoroisopropanol. The results are shown in Table 1. As can be seenfrom Table 1, the relative reactivities are Ti>Sn>Ge, based on either IVor cyclic dimer. Catalyst Amount (ppm) IV Cyclic dimer (wt. %) Ti (OBu)₄73 0.44 2.1 73 0.44 2.1 73 0.44 2.1 Sn (Bu)₂O 72 0.32 1.5 72 0.32 1.5 Ge(OEt)₄ 76 0.19 0.5 76 0.22 0.6

[0064] For comparison, polymerization reactions were also performedusing classical equipment. The same relative reactivities were obtained.However, the total experimental time for one polymerization, includingsetup and work up, took at least six hours. Furthermore, thepolymerization reactions were performed using more than 100 g oligomerper reaction.

EXAMPLE 3 Minimizing Temperature Differences between Reaction Cells

[0065] It has been found that, even when using a heat transfer medium ina kettle as described in FIG. 1, the temperature differences betweendifferent reaction cells may even be further minimized. To this end aspecial arrangement of reaction cells is proposed according to thepresent invention, e.g. as shown in FIG. 3 and FIG. 4.

[0066] The person skilled in the art will understand that manymodifications may be made.

1. Method for screening of polycondensation catalysts, wherein at leasttwo polycondensation catalysis reactions are performed simultaneouslyunder substantially equivalent conditions in at least two reactioncells, using a sample comprising material to be polycondensated and acatalyst to be screened, and wherein the performances of the catalystsare analyzed, characterized in that the polycondensation reactions areperformed in the at least two reaction cells which are present in onereaction room; the reaction room is heated such that the reaction cellsin the reaction room have, at least temporarily, a substantiallyequivalent temperature of a value>150° C.; the reaction room isdepressurized such that in the reaction room, at least temporarily, areduced pressure<100 mbar is maintained; and in each separate reactioncell a pre-selected amount of sample is used in the form of a film on asurface of the reaction cell such that a ratio of sample weight toreaction cell surface area covered with said film of less than 1 g/cm²is obtained.
 2. Method according to claim 1, wherein the reaction roomis heated such that the reaction cells in the reaction room have asubstantially equivalent temperature of a value between 200-320° C.,preferably 230-300° C.
 3. Method according to claim 1 or 2, wherein thereaction cells are arranged such that the temperature in each of the atleast two reaction cells is maintained substantially equivalent. 4.Method according to any of the preceding claims, wherein the reactionroom is depressurized such that, at least temporarily, a reducedpressure below 10 mbar is maintained, more preferably below 5 mbar, mostpreferably a value between 0.01-2 mbar.
 5. Method according to any ofthe preceding claims, wherein the polycondensation reactions areperformed such that in each separate reaction cell a ratio of sampleweight to reaction cell surface area covered with said film of less than0.5 g/cm² is obtained, preferably of less than 0.2 g/cm².
 6. Methodaccording to any of the preceding claims, wherein in each separatereaction cell a pre-selected amount of less than 2 g sample, preferablyless than 1 g, more preferably between 100 mg and 1 mg sample is used.7. Apparatus suitable for performing the method according to any of thepreceding claims 1-6, the apparatus comprising: a sealable reaction roomcontaining at least two reaction cells; vacuum means for providing areduced pressure of<100 mbar in the reaction room; heating means forproviding a reduced temperature of>150° C. in the reaction cells,wherein the at least two reaction cells are arranged such that asubstantially equivalent temperature in substantially all reaction cellscan be maintained.
 8. Apparatus according to claim 7, wherein thereaction cells are arranged in a row.
 9. Apparatus according to claim 8,wherein the reaction cells are arranged in two rows.
 10. Apparatusaccording to claim 9, wherein the reaction cells are arranged in twosets of two rows which two sets are spaced with a suitable distance suchthat a substantially equivalent temperature in substantially allreaction cells can be maintained.
 11. Apparatus according to claim 7,wherein the reaction cells are placed in a circular arrangement withinthe reaction room.
 12. Apparatus according to claim 12, wherein thereaction cells are arranged in two concentric circles.
 13. Apparatusaccording to claim 11 or 12, wherein the reaction cells are placedaround a projection.
 14. Apparatus according to any of the precedingclaims 7-13, wherein the at least two reaction cells are held in a rack.15. Use of the apparatus according to any of the preceding claims 7-14in screening of polycondensation catalysts.